The present invention relates to a liquid crystal display apparatus and, more particularly, to a liquid crystal display apparatus designed so that the viewing angle dependence is minimized without causing the displayed image to become unsharp.
A typical liquid crystal display apparatus has a liquid crystal cell sandwiched between two polarizing plates, in which transmitted light is on/off controlled by controlling an electric field applied to the liquid crystal cell, thereby displaying an image. However, since the viewing angle dependence of the liquid crystal display apparatus is high, the displayed image can be seen only within a specific angle range. Accordingly, the conventional practice is to provide a plurality of recesses and projections on the viewing side the display surface of the liquid crystal display apparatus so as to diffuse light rectilinearly propagated through the liquid crystal layer, thereby reducing the viewing angle dependence [see Japanese Utility Model Application Public Disclosure (KOKAI) No. 04-72221 (1992)].
FIG. 10 is an exploded perspective view of a conventional color liquid crystal display apparatus that uses a twisted nematic (TN) liquid crystal. As shown in the figure, constituent elements are arranged in the following order from the light source side: a light source 1, a polarizing plate 5, a glass plate 6, an electrode plate 9, a liquid crystal layer 7, an electrode plate 9, a glass plate 6, a polarizing plate 5, a color filter 3, and a diffusing member 4 composed of a large number of small transparent projections or recesses. The liquid crystal layer 7 is formed by using a TN liquid crystal, that is, a nematic liquid crystal in which the liquid crystal molecules have been twisted 90.degree.. All the constituent elements except for the light source 1 are laid one on top of another in one unit. Either of the two electrode plates 9 is divided in units of pixels, and the liquid crystal layer 7 is functionally divided into liquid crystal cells corresponding to the divided regions of the electrode plate 9. For each liquid crystal cell, one color filter portion of the color filter 3 is disposed correspondingly.
In the above-described liquid crystal display apparatus, light emitted from the light source 1 is linearly polarized in a predetermined direction by the light source-side polarizing plate 5, and enters the liquid crystal layer 7 where the plane of polarization of the incident light is rotated according to the state of the liquid crystal layer 7. That is, when no voltage is applied to the liquid crystal layer 7, the liquid crystal molecules remain twisted 90.degree.. Then, the light having the plane of polarization rotated according to the twist of the liquid crystal layer 7 reaches another polarizing plate 5. In a case where the transmission axis of this polarizing plate 5 is perpendicular to that of the light source-side polarizing plate 5, the light passes through the polarizing plate 5 and reaches the diffusing member 4 through the color filter 3. At the diffusing member 4, the light is diffused to some extent by a large number of small transparent projections or recesses, thereby enabling the viewing angle to be enlarged. Thus, the viewing angle dependence of the liquid crystal display apparatus decreases. It should be noted that in a case where the two polarizing plates 5 are disposed with their transmission axes perpendicularly intersecting each other as described above, when a voltage is applied to the liquid crystal layer 7, the major axes of the liquid crystal molecules are aligned approximately perpendicular to the liquid crystal layer 7. Consequently, the incident light passes through the liquid crystal layer 7 without rotation of the plane of polarization, and hence it is blocked by the second polarizing plate 5. Thus, the portion where the light is blocked is displayed as a dark. It should be noted that the configuration of each projection or recess of the diffusing member 4 may be either a convex lens configuration as shown, for example, in the perspective and sectional views of FIGS. 11(A) and 11(B), or a convex lens configuration as shown in the perspective and sectional views of FIGS. 11(C) and 11(D).
In the above-described arrangement, however, a glass plate 6 that sandwiches the liquid crystal layer 7 in cooperation with another glass plate 6 is present between the liquid crystal layer 7 and the diffusing member 4. Since the glass plate 6 has a thickness, the diffusing surface of the diffusing member 4 must be disposed apart from the liquid crystal layer 7. Consequently, the displayed image becomes unsharp owing to the diffusing member 4 disposed apart from the display surface.